In a number of current artificial system, information processing and its operations are carried out in accordance with timing steps synchronized with clock signals. In keeping up with the tendency towards an enlarged scale, diversification and networking of systems, an entire system is made up of a set of plural sub-systems, such that more and more importance is attached to the synchronization technique between these sub-systems.
There are a number of fields for application of the synchronization technique, such as large scale integrated circuits (system-on-chips), communication systems inclusive of the Internet, power systems, parallel processing systems and microwave oscillation systems. As a principle, the synchronization technique may be grasped as being the common technique used for synchronization among plural sub-systems.
In a large-scale integrated circuit, for example, a phase locked loop (PLL) or a delay locked loop (DLL) is built on a chip and external clocks are distributed to sub-circuits provided on the chip to realise synchronization among the sub-circuits, as stated in 1996 IEEE ISSCC Proc. (IEEE 1996).
With the increasing scale of the integrated circuits, and with the increasing processing speed, that is clock frequency, difficulties met in clock distribution and phase synchronization designing techniques are increasing. That is, in distributing high-quality high-speed pulse signals to a fine high-density structure over a wide range, increasing energy consumption, lowering in reliability, such as in signal value, timing, lowering in frequency margin etc, overhead due to increasing complexity of the synchronization circuit and increasing difficulties in designing due to the increasing circuit scale, are presenting serious problems. This is the problem common to the above-described diversified fields of application of the integrated circuit.
With regard to an oscillation system, variety of different circuits of a self-excited oscillation system, are known up to now.
The self-excited oscillation system is a system in which oscillations are excited therein on application of a pre-set energy thereto, and may be frequently seen in a fractional oscillation system or an electric oscillation circuit. One of the well-known examples of the self-excited oscillation systems is the van der Pol circuit.
However, with the conventional self-excited oscillation systems, oscillations are self started for any external inputs, as the name implies, with the oscillations, once started, being unable to be terminated. In this sense, there lacks in the conventional self-excited oscillation systems a switching function adapted to control the oscillation on/off. Thus, it is impossible to on/off control the self-excited oscillation of a self-excited oscillation system under a pre-set external input.